Stacked Chip Package With Redistribution Lines

ABSTRACT

A chip package comprises a first chip having a first side and a second side, wherein said first chip comprises a first pad, a first trace, a second pad and a first passivation layer at said first side thereof, an opening in said first passivation layer exposing said first pad, said first trace being over said first passivation layer, said first trace connecting said first pad to said second pad; a second chip having a first side and a second side, wherein said second chip comprises a first pad at said first side thereof, wherein said second side of said second chip is joined with said second side of side first chip; a substrate joined with said first side of said first chip or with said first side of said second chip; a first wirebonding wire connecting said second pad of said first chip and said substrate; and a second wirebonding wire connecting said first pad of said second chip and said substrate.

This application is a continuation of application Ser. No. 11/416,134, now pending which claims the priority benefit of Taiwan application Ser. No. 094114203, filed on May 3, 2005.

FIELD OF THE INVENTION

The invention relates in general to a stacked chip package and a process for forming the same. More particularly, the invention relates to a stacked chip package, wherein the pad position of the chip for wires through wire bonding can be changed through redistribution lines and a process for forming the same.

DESCRIPTION OF THE RELATED ART

Nowadays, advanced data processing and communication play an important role in the modern society. In order to fulfill the requirements of electronic devices, such as high speed processing, multifunction tasks, integration, small size and light weight . . . etc, the package technology of the integrated circuit is developed towards micro-size and high density. For example, Chip Scale Package (CSP), Flip Chip Package and Multi-Chip Module (MCM) Package have emerged.

In Multi-Chip Module package, multiple chips with different or same function are packaged on a carrier, such as a substrate or a lead frame, which is connected electrically to external circuit. For instance, the stacked chip package is one of common Multi-Chip Module. In the stacked chip package, multiple same chips are stacked and then encapsulated in a package to enhance the efficiency of performance by means of the integration of the same chips. The stacked chip package not only can offer the higher transmission speed, that is, the shorter transmission path, the better electronic performance, but can also reduce the size of chip package and its area. Therefore, the stacked chip package has been generally applied in many various electronic products and will become the main stream of chip package in the future.

For example in Dynamic Random Access Memory, DRAM, multiple chips, which have the same size of the memory storage, can be integrated in one package on base of the stacked chip package to improve the processing speed. In addition, the stacked chip package will not cause a really dramatic change of package appearance, so that the package density can be increased and the occupied space can be reduced. Moreover, in the stacked chip package, it is not necessary to renew the design of the circuit layout. It can also provide a better efficiency of processing. As a result, it can decrease the cost of the research dramatically and enhance competitiveness of a product in the market.

Referring to FIG. 1 and FIG. 2, showing cross-sectional views of two traditional stacked chip packages with a window ball grid array (BGA) type, in the stacked chip package 100, two semiconductor chips with a same type, first semiconductor chip 110 and second semiconductor chip 120, are stacked back to back and then are electrically connected to a substrate 130 using a wire bonding process and connected outwardly through a solder ball 190 on the substrate 130. As shown in FIG. 1 and FIG. 2, the first chip 110 is provided with a first active surface 110 a and a corresponding first back surface 110 b. The second chip 120 is provided with a second active surface 120 a and a corresponding second back surface 120 b. The first chip 110 and the second chip 120 are stacked with the first back surface 110 b being in contact with the second back surface 120 b. The substrate 130 is provided with a top surface 130 a and a corresponding bottom surface 130 b. There are multiple first pads 132 on the top surface 130 a and multiple second pads 134 on the bottom surface 130 b. There is an opening in the center of the substrate 130. The first chip 110 is located on the substrate 130 with the first active surface 110 a of the first chip 110 facing the top surface 130 a of the substrate 130.

As above mentioned, because the positions of pads on a semiconductor chip are different, the wires through wire bonding between the semiconductor chip and a substrate are arranged differently. As shown in FIG. 1, the chip pads 122 of the second chip 120 are located in the central region thereof and connected to the first pads 132 of the substrate 130 through multiple second wires 160 formed by a wire bonding process. The first chip pads 112 of the first chip 110 are located in the central region of the first active surface 110 a thereof. The first wires 150 formed by a wire bonding process go through the opening 136 and connect the first chip pads 112 and the second pads 134 of the substrate 130. In order to connect the second chip 120 and the substrate 130, the second wires 160 formed by a wire bonding process has to go from the central region of the second active surface 120 a to the top surface 130 a of the substrate 130. The second wires 160 are so long that the electrical performance of signal transmitted between the second chip 120 and the substrate 130 is negatively affected.

As shown in FIG. 2, the first chip pads 112 of the first semiconductor chip 110 are located in the peripheral region of the first active surface 110 a. Similarly, the second chip pads 122 of the second chip 120 are located in the peripheral region of the second active surface 120 a. Thereby, the second wires 160 formed by a wirebonding process may have a reduced distance between the chip pads 122 of the second chip 120 and the first pads 132 of the substrate 130. However, the first chip pads 112 of the first chip 110 are blocked by the substrate 130, so that it cannot be connected to the second pads 134 of the substrate 130 by using a wirebonding process.

To solve the problems mentioned above, it is known that the first chip and the second chip ought to be provided with different pad layout exposed by openings in a passivation layer comprising nitride. For example, the chip pads of the first chip exposed by openings in a passivation layer comprising nitride can be located in the central region of the active surface and the chip pads of the second chip exposed by openings in a passivation layer comprising nitride can be located in the peripheral region of the active surface. However, if they are changed in this way, the electric devices or circuits formed inside the semiconductor chip has to be rerouted. This change of rerouting the electric devices and circuits takes a lot of effort, but just develops a semiconductor chip with same functions. It cannot meet the requirement for lowering production costs.

SUMMARY OF THE INVENTION

Therefore, one objective of the present invention is to provide a chip package with shorter wirebonding wires. A better electric performance of transmitting signals through the wirebonding wires can be achieved.

Furthermore, multiple pads of a semiconductor chip blocked by a substrate can be avoided and it is not needed to redesign the circuit layout under a passivation layer of the semiconductor chip.

In order to reach the above objectives, the present invention provides a chip package comprising a first semiconductor chip having a first side and a second side, wherein said first semiconductor chip comprises a first pad, a first trace, a second pad and a first passivation layer at said first side thereof, an opening in said first passivation layer exposing said first pad, said first trace connecting said first pad to said second pad, the position of said second pad from a top view being different that of said first pad; a second semiconductor chip having a first side and a second side, wherein said second semiconductor chip comprises a first pad at said first side thereof, wherein said second side of said second semiconductor chip is joined with said second side of side first semiconductor chip; a substrate joined with said first side of said first semiconductor chip or with said first side of said second semiconductor chip; a first wirebonding wire connecting said second pad of said first semiconductor chip and said substrate; and a second wirebonding wire connecting said first pad of said second semiconductor chip and said substrate.

Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive to the invention, as claimed. It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated as a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 and FIG. 2 show cross-sectional views of two traditional stacked chip packages with a window ball grid array (BGA) type.

FIG. 3 through FIG. 6 schematically show a process for fabricating a stacked chip package in a first embodiment of the present invention.

FIG. 7 shows a schematic view of a stacked chip package structure according to a first embodiment.

FIG. 8A through FIG. 8C are schematic cross-sectional views showing various metallization structure of the first redistribution lines 340.

FIG. 9 to FIG. 12 are schematically cross-sectional views showing a process for fabricating a stacked chip package structure according to a second embodiment of the present invention.

FIG. 13 shows a schematic view of a stacked chip package structure according to a second embodiment.

FIG. 14 is a cross-sectional view of a stacked chip package according to a third embodiment.

FIG. 15 and FIG. 16 are schematically cross-sectional views of two stacked chip packages according to a fourth embodiment.

FIG. 17A through the FIG. 17D are enlarged views showing a semiconductor chip with a polymer layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 3 through FIG. 6 schematically show a process for fabricating a stacked chip package in a first embodiment of the present invention. Referring to FIG. 3 through FIG. 6, a first semiconductor chip 310 and second semiconductor chip 320 are provided with a same circuit layout under first and second passivation layers 314 and 324 thereof. The first semiconductor chip 310 is provided with multiple first chip pads 312 located on a first active surface 310 a of the first chip 310. The first chip pads 312 are located in the peripheral region of the first active surface 310 a. The first passivation layer 314 has multiple openings 314 a for exposing the first chip pads 312. The second semiconductor chip 320 is provided with multiple second chip pads 322 located on a second active surface 320 a of the second chip 320. The second chip pads 322 are located in the peripheral region of the second active surface 320 a. The second passivation layer 324 has multiple openings 324 a for exposing the second chip pads 322.

In a case, each of the first and second passivation layers 314 and 324 can be formed by first depositing a silicon-oxide layer with a thickness of between 0.2 and 0.7 microns using a PECVD process, then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the silicon-oxide layer using a PECVD process.

In another case, each of the first and second passivation layers 314 and 324 can be formed by first depositing a silicon-oxide layer with a thickness of between 0.2 and 0.7 microns using a PECVD process, then depositing a silicon-oxynitride layer with a thickness of between 0.05 and 0.15 microns on the silicon-oxide layer using a PECVD process, and then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the silicon-oxynitride layer using a PECVD process.

In another case, each of the first and second passivation layers 314 and 324 can be formed by first depositing a silicon-oxynitride layer with a thickness of between 0.05 and 0.15 microns using a PECVD process, then depositing a silicon-oxide layer with a thickness of between 0.2 and 0.7 microns on the silicon-oxynitride layer using a PECVD process, and then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the silicon-oxide layer using a PECVD process.

In another case, each of the first and second passivation layers 314 and 324 can be formed by first depositing a silicon-oxide layer with a thickness of between 0.2 and 0.5 microns using a PECVD process, then depositing a silicon-oxide layer with a thickness of between 0.5 and 1 microns on the PECVD silicon-oxide layer using a spin-coating process, then depositing a silicon-oxide layer with a thickness of between 0.2 and 0.5 microns on the spin-coated silicon-oxide layer using a PECVD process, and then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the PECVD silicon-oxide layer using a PECVD process.

In another case, each of the first and second passivation layers 314 and 324 can be formed by first depositing a silicon-oxide layer with a thickness of between 0.5 and 2 microns using a HDP-CVD process, and then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the silicon-oxide layer using a PECVD process.

In another case, each of the first and second passivation layers 314 and 324 can be formed by first depositing a USG layer with a thickness of between 0.2 and 3 microns, then depositing a layer of TEOS, BPSG or PSG with a thickness of between 0.5 and 3 microns on the USG layer, and then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the layer of TEOS, BPSG or PSG using a PECVD process.

In another case, each of the first and second passivation layers 314 and 324 can be formed by optionally first depositing a first silicon-oxynitride layer with a thickness of between 0.05 and 0.15 microns using a PECVD process, then depositing a silicon-oxide layer with a thickness of between 0.2 and 0.7 microns optionally on the first silicon-oxynitride layer using a PECVD process, then optionally depositing a second silicon-oxynitride layer with a thickness of between 0.05 and 0.15 microns on the silicon-oxide layer using a PECVD process, then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the second silicon-oxynitride layer or on the silicon-oxide layer using a PECVD process, then optionally depositing a third silicon-oxynitride layer with a thickness of between 0.05 and 0.15 microns on the silicon-nitride layer using a PECVD process, and then depositing a silicon-oxide layer with a thickness of between 0.2 and 0.7 microns on the third silicon-oxynitride layer or on the silicon-nitride layer using a PECVD process.

In another case, each of the first and second passivation layers 314 and 324 can be formed by first depositing a first silicon-oxide layer with a thickness of between 0.2 and 0.7 microns using a PECVD process, then depositing a second silicon-oxide layer with a thickness of between 0.5 and 1 microns on the first silicon-oxide layer using a spin-coating process, then depositing a third silicon-oxide layer with a thickness of between 0.2 and 0.7 microns on the second silicon-oxide layer using a PECVD process, then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the third silicon-oxide layer using a PECVD process, and then depositing a fourth silicon-oxide layer with a thickness of between 0.2 and 0.7 microns on the silicon-nitride layer using a PECVD process.

In another case, each of the first and second passivation layers 314 and 324 can be formed by first depositing a silicon-oxide layer with a thickness of between 0.5 and 2 microns using a HDP-CVD process, then depositing a silicon-nitride layer with a thickness of between 0.2 and 0.7 microns on the silicon-oxide layer using a PECVD process, and then depositing another silicon-oxide layer with a thickness of between 0.5 and 2 microns on the silicon-nitride layer using a HDP-CVD process.

A description of the stacked chip package structure of the present invention is as follows:

First, as shown in FIG. 3, multiple first redistribution lines 340 are formed on the first passivation layer 314 of a first semiconductor wafer. After cutting the first semiconductor wafer, multiple individual first semiconductor chips 310 with the first redistribution lines 340 on the first passivation layer 314 are formed. The first redistribution lines 340 have multiple pads 342 electrically connected to the first chip pads 312. These pads 342 of the first redistribution lines are located in the central region of the first semiconductor chip 310.

Next, as shown in FIG. 4, the first semiconductor chip 310 is being mounted on a substrate 330, such as printed circuit board, flexible substrate with only one circuit layer and only one polymer layer formed on the circuit layer, ceramic substrate, or glass substrate. The substrate 330 has multiple first substrate pads 332 and multiple second substrate pads 334 located on a top surface 330 a and a bottom surface 330 b of the substrate 330, respectively. An opening 336 in the substrate 330 passes through the substrate 330. The first active surface 310 a of the first chip 310 is adhered to the top surface 330 a of the substrate 330. The first redistribution pads 342 are exposed by the opening 336 in the substrate 330.

Subsequently, as shown in FIG. 5, the back surface 320 b of the second chip 320 is back to back joined to the back surface 310 b of the first chip 310.

Next, as shown in FIG. 6, a wire bonding process is performed to form multiple first wires 350 connecting the first redistribution pads 342 and the second substrate pads 334 through the opening 336 in the substrate 330 and to form multiple second wires 360 connecting the second chip pads 322 and the first substrate pads 332. Afterwards, an encapsulation process is performed to form a first molding compound 370 in the opening 136 in the substrate 330 and on the bottom surface 330 b of the substrate 330 and to form a second molding compound 380 on the second semiconductor chip 320 and on the top surface 330 a of the substrate 330. The first molding compound 370 and the second molding compound 380 enclose the first wires 350 and the second wires 360, respectively. The first molding compound 370 and the second molding compound 380 maybe a thermosetting polymer or a thermoplastic polymer.

Two points are especially worthy of notice.

First, the order of two steps described in FIG. 4 and FIG. 5 can be interchangeable. Specifically, the first chip 310 and the second chip 320 can be first joined to each other, and then the unity of the first chip 310 and the second chip 320 can be disposed onto the substrate 330.

Second, as shown in FIG. 6, the wire bonding process and the encapsulating process can be performed in other sequences. For example, the process for fabricating the chip package can be performed by first wirebonding the first wires 350, next forming the first molding compound 370, next wirebonding the second wires 360, and then forming the second molding compound 380. Alternatively, the process for fabricating the chip package can be performed by first wirebonding the second wires 360, next forming the second molding compound 380, next wirebonding the first wires 350, and then forming the first molding compound 370. The first wires 350 and the second wires 360 may comprise gold. Alternatively, the process for fabricating the chip package can be performed by first wirebonding the first wires 350 and the second wires 360, and then forming the first molding compound 370 and the second molding compound 380.

In the embodiment above mentioned, the main components of the stacked chip package structure of the present invention have been illustrated. However, in the practical situation, the process for fabricating a stacked chip package may include other steps. For example, multiple sold balls may be formed on the bottom surface of the substrate; a polymer layer may be formed on the passivation layer; a polymer layer may be formed on the redistribution lines. The redistribution structure may be composed of not only a single patterned circuit layer, as shown in FIG. 6 but multiple patterned circuit layers.

FIG. 7 shows a schematic view of a stacked chip package structure according to a first embodiment. The reference number in FIG. 7 indicates the same part or the like as those indicated by the same reference number in FIGS. 3-6. The description of the arrangement of the substrate 330, the first and second semiconductor chips 310 and 320, the first and second wires 350 and 360 formed by a wire bonding process, and the first and second molding compound 370 and 380 can be referred to the above illustration.

As shown in FIG. 7, the stacked chip package 300 may include the first semiconductor chip 310, the second semiconductor chip 320, the substrate 330, the first redistribution lines 340, the first and second wires 350 and 360 formed by a wire bonding process, the first and second molding compound 370 and 380, and multiple solder balls 390. The first semiconductor chip 310 and the second semiconductor chip 320 stacked back to back are disposed on the substrate 330. The first redistribution lines 340 are disposed on the first passivation layer 314 of the first chip 310 and provide multiple first redistribution pads 342 that are located in the central region of the first semiconductor chip 310 and electrically connected to the substrate pads 334 through the first wires 350 formed by a wire bonding process. Multiple solder balls 390 are disposed on the bottom surface 330 b of the substrate 330 and serves as the means for the electrical connection of the first chip 310 and the second chip 320 to an external circuit. The material of the solder ball can include an alloy of tin and lead or an alloy of tin, silver and cooper.

Referring to FIG. 7, the thicknesses s1 and s2 of the first passivation layer 314 and the second passivation layer 324 are more than 0.35 micrometer. The passivation layer may be constructed of a silicon nitride compound, a silicon oxide compound, a phosphosilicate glass (PSG), or a composite including at least one of the above materials.

It is remarkable that the first redistribution lines 340 of the present invention can be constructed of one or multiple patterned circuit layers. Various structures and materials can be applied to the patterned circuit layers. For example, the first redistribution lines 340 formed from a single patterned circuit layer is shown in FIG. 7. The thickness t of the redistribution lines 340 is larger than 1 micrometer. FIG. 8A through FIG. 8C are schematic cross-sectional views showing various metallization structure of the first redistribution lines 340.

As above mentioned and as shown in FIG. 8A, the first redistribution lines 340 are constructed of one layer or multiple layers of well-conductive metal and an adhesion/barrier layer. The adhesion/barrier layer is made of a titanium layer, an alloy layer of titanium and tungsten or a composite of a chromium layer and an alloy layer of chromium and copper. According to an embodiment in FIG. 8A, the adhesion/barrier layer 14 is an alloy layer of titanium and tungsten and the metal layer 12 is a gold layer with a thickness of between 1 and 15 microns. In addition, as shown in FIG. 8B, the first redistribution lines 340 can be constructed of a titanium layer 28, a copper layer 26 with a thickness of between 1 and 30 microns, a nickel layer 24 with a thickness of between 1 and 10 microns, and a gold layer 22. The titanium or chromium layer 28 is used for the adhesion/barrier layer. The gold layer 22 and the nickel layer 24 can be optionally formed onto the copper layer 26. Moreover, as shown in FIG. 8C, the first redistribution lines can be a single layer of aluminum 32.

Second Embodiment

According to the above mentioned first embodiment, the redistribution lines are disposed on the first semiconductor chip in order to avoid the chip pads in the peripheral region of the first semiconductor chip being blocked by the substrate and to solve the incapability of being wirebonded to the first chip.

Similarly, the present invention can solve the problem of the wires formed by a wire bonding process being too long in case that the chip pads of the first and second semiconductor chips are located in the central region thereof.

FIG. 9 to FIG. 12 are schematically cross-sectional views showing a process for fabricating a stacked chip package structure according to a second embodiment of the present invention. As shown from FIG. 9 to FIG. 12, first and second semiconductor chips 410 and 420 are provided with a same circuit layout under first and second passivation layers 414 and 424 thereof. The first chip 410 has multiple first chip pads 412 in a central region of thereof. The first passivation layer 414 on the first active surface 410 a has multiple openings 414 a for exposing the first pads 412. The second chip 420 is provided with multiple second chip pads 422 and the second passivation layer 424 on the second active surface 420 a of the second chip 420. The second chip pads 422 are located in the central region of the second chip 420. The second passivation layer 424 has multiple openings 424 a to expose the second chip pads 422.

A description for a stacked chip package structure of the present invention is as follows:

First, as shown in FIG. 9, multiple second redistribution lines 440 are formed on the second passivation layer 424 of a second semiconductor wafer. After cutting the second semiconductor wafer, multiple individual second semiconductor chips 420 with the second redistribution lines 440 on the second passivation layer 424 are formed. The second redistribution lines 440 have multiple pads 442 electrically connected to the second chip pads 422. The pads 442 of the second redistribution lines 440 are located in the peripheral region of the second semiconductor chip 420.

Next, as shown in FIG. 10, the first semiconductor chip 410 is being mounted on a substrate 430, such as printed circuit board, flexible substrate with only one circuit layer and only one polymer layer formed on the circuit layer, ceramic substrate, or glass substrate. The substrate 430 has multiple first substrate pads 432 and multiple second substrate pads 434 located on a top surface 430 a and a bottom surface 430 b of the substrate 430, respectively. An opening 436 in the substrate 430 passes through the substrate 430. The first active surface 410 a of the first chip 410 is adhered to the top surface 430 a of the substrate 430. The first chip pads 412 are exposed by the opening 436 in the substrate 430.

Next, as shown in FIG. 11, the back surface 420 b of the second chip 420 is back to back joined to the back surface 410 b of the first chip 410.

Subsequently, as shown in FIG. 12, a wire bonding process is performed to form multiple first wires 450 connecting the first chip pads 412 and the second substrate pads 434 through the opening 436 in the substrate 430 and to form multiple second wires 460 connecting the second redistribution pads 442 and the first substrate pads 432. Afterwards, an encapsulation process is performed to form a first molding compound 470 in the opening 436 in the substrate 430 and on the bottom surface 430 b of the substrate 430 and to form a second molding compound 480 on the second semiconductor chip 420 and on the top surface 430 a of the substrate 430. The first molding compound 470 and the second molding compound 480 enclose the first wires 450 and the second wires 460, respectively. The first molding compound 470 and the second molding compound 480 maybe a thermosetting polymer or a thermoplastic polymer.

As mentioned in the first embodiment of the present invention, the order of two steps described in FIG. 10 and FIG. 11 can be interchangeable. Specifically, the first chip 410 and the second chip 420 can be first joined to each other, and then the unity of the first chip 410 and the second chip 420 can be disposed onto the substrate 430.

Second, as shown in FIG. 12, the wire bonding process and the encapsulating process can be performed in other sequences. For example, the process for fabricating the chip package can be performed by first wirebonding the first wires 450, next forming the first molding compound 470, next wirebonding the second wires 460, and then forming the second molding compound 480. Alternatively, the process for fabricating the chip package can be performed by first wirebonding the second wires 460, next forming the second molding compound 480, next wirebonding the first wires 450, and then forming the first molding compound 470. Alternatively, the process for fabricating the chip package can be performed by first wirebonding the first wires 450 and the second wires 460, and then forming the first molding compound 470 and the second molding compound 480.

FIG. 13 shows a schematic view of a stacked chip package structure according to a second embodiment. The reference number in FIG. 13 indicates the same part or the like as those indicated by the same reference number in FIGS. 9-12. The description of the arrangement of the substrate 430, the first and second semiconductor chips 410 and 420, the first and second wires 450 and 460 formed by a wire bonding process, and the first and second molding compound 470 and 480 can be referred to the above illustration.

As shown in FIG. 13, the stacked chip package structure 400 may include the first semiconductor chip 410, the second semiconductor chip 420, the substrate 430, the second redistribution lines 440, the first and second wires 450 and 460 formed by a wirebonding process, the first and second molding compound 470 and 480, and the solder ball 490. The first semiconductor chip 410 and the second semiconductor chip 420 stacked back to back are disposed on the substrate 430. The second redistribution lines 440 are disposed on the second passivation layer 424 of the second semiconductor chip 420 and provide multiple second redistribution pads 442 that are located in the peripheral region of the second semiconductor chip 420 and electrically connected to the substrate pads 432 through the second wires 460 formed by a wirebonding process, and thereby the second wires 460 may have a reduced length. Multiple solder balls 490 are disposed on the bottom surface 430 b of the substrate 430 and used for the electrical connection of the first chip 410 and the second chip 420 to an external circuit. The material of the solder balls 490 can be an alloy of tin and lead or an alloy of tin, silver and cooper.

It should be noted that the first and second passivation layers 414 and 424 may have a same material or structure as those of the first and second passivation layers 314 and 324 as described in the first embodiment. The second redistribution lines 440 may have a same material or structure as those of the first redistribution lines 340 as described in the first embodiment. The substrate 430 may have a same material or structure as those of the substrate 330 as described in the first embodiment.

Third Embodiment

According to the above mentioned first and second embodiments, the first semiconductor chip and the second semiconductor chip have a same circuitry layout under the passivation layer. The first chip pads and the second chip pads that are in same positions have same electrical functions. However, in other embodiments of the present invention, the first semiconductor chip and the second semiconductor chip may have different circuitry layouts.

FIG. 14 is a cross-sectional view of a stacked chip package according to a third embodiment. As shown in FIG. 14, multiple first chip pads 512 of a first semiconductor chip 510 exposed by multiple openings in a first passivation layer 514 are disposed in the peripheral region of the first semiconductor chip 510 and are blocked by a substrate 530. Multiple second chip pads 522 of a second semiconductor chip 520 exposed by multiple openings in a second passivation layer 524 are disposed in the central region of the second semiconductor chip 520. In this embodiment, the first redistribution lines 540 are located on the first passivation layer 514 of the first semiconductor chip 510. The first redistribution lines 540 are electrically connected to the first chip pads 512. Multiple first redistribution pads 542 of the first redistribution lines 540 are located in the central region of the first semiconductor chip 510 and exposed through the opening 536 in the substrate 530. The second redistribution lines 544 are located on the second passivation layer 524 of the second semiconductor chip 520. The second redistribution lines 544 are electrically connected to the second chip pads 522. Multiple second redistribution pads 546 of the second redistribution lines 544 are located in the peripheral region of the second semiconductor chip 520.

Due to the formation of the first and second redistribution lines 540 and 544, multiple first wires 550 formed by a wire bonding process can pass through the opening 536 in the substrate 530 and make an electric connection between the first redistribution pads 542 and the second substrate pads 534. The second wires 560 formed by a wire bonding process can make an electric connection between the second redistribution pads 546 and the first substrate pads 532, and thereby the second wires 560 may have a reduced length.

It should be noted that the first and second passivation layers 514 and 524 may have a same material or structure as those of the first and second passivation layers 314 and 324 as described in the first embodiment. The first and second redistribution lines 540 and 544 may have a same material or structure as those of the first redistribution lines 340 as described in the first embodiment. The substrate 530 may have a same material or structure as those of the substrate 330 as described in the first embodiment.

Fourth Embodiment

Except for the above mentioned embodiments, the chip pads of the first semiconductor chip and the second semiconductor chip can be partially located in the peripheral region of the first and second semiconductor chips and partially located in the central region of the first and second semiconductor chips. FIG. 15 and FIG. 16 are schematically cross-sectional views of two stacked chip packages according to a fourth embodiment. As shown in FIG. 15, partial second chip pads 622 of a second semiconductor chip 620 exposed by multiple openings in a second passivation layer 624 are located in the central region of the second semiconductor chip 620. Partial second chip pads 622 of a second semiconductor chip 620 exposed by multiple openings in a second passivation layer 624 are located in the peripheral region of the second semiconductor chip 620. A patterned circuit layer is formed on the second passivation layer 624 and on the second chip pads 622 in the central and peripheral regions of the second semiconductor chip 620. The patterned circuit layer includes multiple redistribution lines 640 disposed on the second passivation layer 624 and connected to the second chip pads 622 in the central region of the second semiconductor chip 620. The redistribution lines 640 include multiple redistribution pads 642 in the peripheral region of the second semiconductor chip 620, wherein the redistribution pads 642 are connected to the second chip pads 622 in the central region of the second semiconductor chip 620. The patterned circuit layer includes multiple metal pads 644 on the second chip pads 622 in the peripheral region of the second semiconductor chip 620. Multiple second wires 660 a and 660 b formed by a wirebonding process connect the metal pads 642 and 644 of the patterned circuit layer to multiple metal pads 632 a and 632 b on a top surface of a substrate 630. The second wires 660 a are over the second wires 660 b. The second wires 660 a and 660 b are enclosed by a molding compound 680. The first chip pads 612 exposed by multiple openings in a first passivation layer 614 of the first semiconductor chip 610 is provided in a central region of the first semiconductor chip 610. Multiple first wires 650 formed by a wirebonding process may be connected to the first chip pads 612 through an opening 636 in a substrate 630.

It should be noted that the first and second passivation layers 614 and 624 may have a same material or structure as those of the first and second passivation layers 314 and 324 as described in the first embodiment. The patterned circuit layer including the redistribution lines 640 and the metal pads 644 may have a same material or structure as those of the first redistribution lines 340 as described in the first embodiment. The substrate 630 may have a same material or structure as those of the substrate 330 as described in the first embodiment. Other similar structures not mentioned above but shown in FIG. 15 may be as referred to those illustrated in the above first, second and third embodiments.

As shown in FIG. 16, Partial first chip pads 712 of a first semiconductor chip 710 exposed by multiple openings in a first passivation layer 714 are located in the peripheral region of the first semiconductor chip 710. Partial first chip pads 712 of a first semiconductor chip 710 exposed by multiple openings in a first passivation layer 714 are located in the central region of the first semiconductor chip 710. A patterned circuit layer is formed on the first passivation layer 714 and on the first chip pads 712 a and 712 b in the central and peripheral regions of the first semiconductor chip 710. The patterned circuit layer includes multiple redistribution lines 740 disposed on the first passivation layer 714 and connected to the first chip pads 712 a in the peripheral region of the first semiconductor chip 710. The redistribution lines 740 provide multiple redistribution pads 742 in the central region of the first semiconductor chip 710, wherein the redistribution pads 742 are connected to the first chip pads 712 a in the peripheral region of the first semiconductor chip 710. The patterned circuit layer includes multiple metal pads 744 on the first chip pads 712 b in the central region of the first semiconductor chip 710. Multiple first wires 750 a and 750 b formed by a wirebonding process connect the metal pads 742 and 744 of the patterned circuit layer to multiple metal pads 734 a and 734 b on a bottom surface of a substrate 730 through an opening 736 in the substrate 730. The first wires 750 b are over the first wires 750 a. The first wires 750 a and 750 b are enclosed by a molding compound 770. Multiple second chip pads 722 exposed by multiple openings in a second passivation layer 724 of a second semiconductor chip 720 is provided in a peripheral region of the second semiconductor chip 720. Multiple second wires 760 formed by a wirebonding process may connect the second chip pads 722 to a metal pad 732 on a top surface of the substrate 730.

It should be noted that the first and second passivation layers 714 and 724 may have a same material or structure as those of the first and second passivation layers 314 and 324 as described in the first embodiment. The patterned circuit layer including the redistribution lines 740 and the metal pads 744 may have a same material or structure as those of the first redistribution lines 340 as described in the first embodiment. The substrate 730 may have a same material or structure as those of the substrate 330 as described in the first embodiment. Other similar structures not mentioned above but shown in FIG. 16 may be as referred to those illustrated in the above first, second and third embodiments.

To sum up, the stacked chip package and the process for forming the same employ multiple redistribution lines formed on the upper or lower semiconductor chip to change the positions of the metal pads used to be wirebonded thereto. Therefore, multiple chip pads of the lower semiconductor chip used to be wirebonded thereto cannot be blocked by the substrate. If the chip pads of the upper semiconductor chip are too far from the edge of the upper semiconductor chip, multiple redistribution lines can be formed over the upper semiconductor chip to form multiple metal pads used to be wirebonded thereto close to an edge of the upper semiconductor chip, thereby the wires formed by a wirebonding process and connected to the redistributed metal pads may have reduce lengths.

It is remarkable that in the stacked chip package of the present invention, at least one polymer layer can be optionally formed over the first passivation layer of the first semiconductor chip and/or over the second passivation layer of the second semiconductor chip as disclosed in the above mentioned embodiments. FIG. 17A through the FIG. 17D are enlarged views showing a semiconductor chip with a polymer layer. The structure below mentioned in FIG. 17A through FIG. 17D can be applied to the above mentioned first semiconductor chip and/or the second semiconductor chip.

As shown in FIG. 17A, there is a polymer layer 848 disposed on the redistribution lines 840. The material of the polymer layer 848 can be polyimide (PI), benzo-cyclo-butene (BCB), parylene, epoxy or elastomer. The polymer layer 848 may be a solid structure or a porous structure. The thickness m1 of the polymer layer 848 ranges from 1 to 20 microns. The thickness t of the redistribution lines 840 ranges from 1 to 20 microns. The thickness s1 of the passivation layer 814 ranges from 0.3 and 1 microns. The passivation layer 814 is typically constructed of inorganic compounds, such as silicon nitride, silicon oxide, phosphosilicate glass (PSG), or a composite of the above-mentioned materials. The redistribution lines 840 may have a same material or structure as those of the first redistribution lines 340 as described in the first embodiment.

As shown in FIG. 17B, a polymer layer 816 can be formed between the redistribution lines 840 and the passivation layer 814. The material of the polymer layer 816 can be polyimide (PI), benzo-cyclo-butene (BCB), parylene, epoxy or elastomer. The polymer layer 816 may be a solid structure or a porous structure. The thickness m2 of the polymer layer 816 ranges from 1 microns to 20 microns. The thickness t of the redistribution lines 840 ranges from 1 microns to 20 microns. The thickness s1 of the passivation layer 814 ranges from 0.3 and 1 microns. The passivation layer 814 is typically constructed of inorganic compounds, such as silicon nitride, silicon oxide, phosphosilicate glass (PSG), or a composite of the above mentioned materials. The redistribution lines 840 may have a same material or structure as those of the first redistribution lines 340 as described in the first embodiment.

As shown in FIG. 17C, Multiple polymer layers 848 and 816 can be disposed on the redistribution lines 840 and between the redistribution lines 840 and the passivation layer 814, respectively. The material and the thickness of the polymer layers 848 and 816 are the same as those having same reference numbers above mentioned in FIG. 17A and FIG. 17B. The thickness t of the redistribution lines 840 ranges from 1 to 20 microns. The thickness s1 of the passivation layer 814 ranges from 0.3 to 1 microns. The passivation layer 814 is typically constructed of inorganic compounds, such as silicon nitride, silicon oxide, phosphosilicate glass (PSG), or a composite of the above mentioned materials. The redistribution lines 840 may have a same material or structure as those of the first redistribution lines 340 as described in the first embodiment.

In case that the redistribution lines 840 are constructed from multiple patterned circuit layers, the above mentioned polymer layer can be disposed between the patterned circuit layers. As shown in FIG. 17D, the redistribution lines 840 are made from a first patterned circuit layer 840 a and a second patterned circuit layer 840 b. A polymer layer 844 is disposed on the first patterned circuit layer 840 a and its material can be polyimide (PI), benzo-cyclo-butene (BCB), parylene, epoxy or elastomer. The polymer layer 844 can be a solid structure or a porous structure. The thickness m3 of the polymer layer 844 ranges from 1 to 20 microns. The thickness t1 of the patterned circuit layer 840 a and the thickness t2 of the second patterned circuit layer range from 1 to 20 microns. The thickness s1 of the passivation layer 814 ranges from 0.3 to 1 microns. The passivation layer is typically constructed of inorganic compounds, such as silicon nitride, silicon oxide, phosphosilicate glass (PSG), or a composite of the above mentioned materials. Alternatively, a polymer layer can be deposited between the first patterned circuit layer 840 a and the passivation layer 814. The redistribution lines 840 a and 840 b may have a same material or structure as those of the first redistribution lines 340 as described in the first embodiment.

In the stacked chip package of the prevent invention, a polymer layer can be disposed between the passivation layer and the redistribution lines, over the redistribution lines, or between the multiple patterned circuit layers of the redistribution lines. The distribution lines can be constructed from single or multiple patterned circuit layers. Various materials can be employed to the redistribution lines.

To sum up, the stacked chip package and the process for forming the same have at least following advantages:

a. The length of the wires formed by a wirebonding process can be reduced, and thereby a better electric performance of transmitting signals through the wires can be achieved.

b. The chip pads blocked by the substrate can be avoided and it is not needed to redesign the circuit layout under a passivation layer on a semiconductor chip. As a result, the process of forming the semiconductor chip can be simplified.

c. Multiple semiconductor chips with a same circuit layout under passivation layers thereof can be integrated in an electronic package. It is contributive to reduce the production costs and enhance the manufacture efficiency.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. Therefore, the protection area of the present invention depends on the claims attached in the patent application. 

What is claimed is:
 1. A chip package comprising: a substrate; a first semiconductor chip over said substrate, wherein said first semiconductor chip has a first side facing a first side of said substrate, and wherein said first semiconductor chip comprises a first metal pad at said first side of said first semiconductor chip, wherein said first metal pad is connected to a second metal pad of said substrate; a second semiconductor chip over said first semiconductor chip, wherein said second semiconductor chip has a first side facing a second side of said first semiconductor chip, wherein said second side of said first semiconductor chip is opposite to said first side of said first semiconductor chip, and wherein said second semiconductor chip comprises a passivation layer at a second side of said second semiconductor chip, a third metal pad having a contact point at a bottom of an opening in said passivation layer, and a metal layer over said passivation layer and over said third metal pad, wherein said second side of said second semiconductor chip is opposite to said first side of said second semiconductor chip, wherein said passivation layer comprises a nitride layer, wherein said metal layer is connected to said third metal pad through said opening in said passivation layer, and wherein said metal layer comprises a fourth metal pad over said passivation layer, wherein said fourth metal pad is connected to said third metal pad through said opening in said passivation layer, and wherein the position of said fourth metal pad from a top perspective view is different from that of said third metal pad, wherein said second semiconductor chip has a first edge, a second edge opposite to said first edge, and a center point between said first and second edges, wherein a horizontal distance between said fourth metal pad and said first edge is less than that between said third metal pad and said first edge, and a horizontal distance between said third metal pad and said center point is less than that between said third metal pad and said first edge; and a first wirebonded wire connecting said fourth metal pad to a fifth metal pad of said substrate across said first edge, wherein said fifth metal pad is at said first side of said substrate.
 2. The chip package of claim 1 further comprising a second wirebonded wire connecting said first metal pad to said second metal pad through an opening in said substrate, and a polymer in said opening in said substrate, wherein said polymer encloses said second wirebonded wire, wherein said first semiconductor chip is over said opening in said substrate, and wherein said second metal pad is at a second side of said substrate, wherein said second side of said substrate is opposite to said first side of said substrate.
 3. The chip package of claim 1 further comprising a solder ball joined with a second side of said substrate, wherein said second side of said substrate is opposite to said first side of said substrate.
 4. The chip package of claim 1 further comprising a polymer over said first side of said substrate, wherein said polymer encloses said first wirebonded wire.
 5. The chip package of claim 1, wherein said nitride layer has a thickness between 0.2 and 0.7 micrometers.
 6. The chip package of claim 1, wherein said metal layer comprises a titanium-containing layer and a gold layer on said titanium-containing layer, wherein said gold layer has a thickness between 1 and 15 micrometers.
 7. The chip package of claim 1, wherein said metal layer comprises a copper layer and a nickel layer on said copper layer, wherein said copper layer has a thickness between 1 and 30 micrometers, and wherein said nickel layer has a thickness between 1 and 10 micrometers.
 8. The chip package of claim 7, wherein said metal layer further comprises a gold layer on said nickel layer.
 9. The chip package of claim 1, wherein said first wirebonded wire comprises gold.
 10. A chip package comprising: a substrate; a first semiconductor chip over said substrate, wherein said first semiconductor chip has a first side facing a first side of said substrate, and wherein said first semiconductor chip comprises a first metal pad at said first side of said first semiconductor chip, wherein said first metal pad is connected to a second metal pad of said substrate; a second semiconductor chip over said first semiconductor chip, wherein said second semiconductor chip has a first side facing a second side of said first semiconductor chip, wherein said second side of said first semiconductor chip is opposite to said first side of said first semiconductor chip, and wherein said second semiconductor chip comprises a passivation layer at a second side of said second semiconductor chip, a third metal pad having a contact point at a bottom of an opening in said passivation layer, and a metal layer over said passivation layer and over said third metal pad, wherein said second side of said second semiconductor chip is opposite to said first side of said second semiconductor chip, wherein said passivation layer comprises a nitride layer having a thickness between 0.2 and 0.7 micrometers, wherein said metal layer comprises a titanium-containing layer and a gold layer on said titanium-containing layer, wherein said gold layer has a thickness between 1 and 15 micrometers, wherein said metal layer is connected to said third metal pad through said opening in said passivation layer, and wherein said metal layer comprises a fourth metal pad over said passivation layer, wherein said fourth metal pad is connected to said third metal pad through said opening in said passivation layer, and wherein the position of said fourth metal pad from a top perspective view is different from that of said third metal pad, wherein said second semiconductor chip has a first edge, a second edge opposite to said first edge, and a center point between said first and second edges, wherein a horizontal distance between said fourth metal pad and said first edge is less than that between said third metal pad and said first edge, and a horizontal distance between said third metal pad and said center point is less than that between said third metal pad and said first edge; and a first wirebonded wire connecting said fourth metal pad to a fifth metal pad of said substrate across said first edge, wherein said fifth metal pad is at said first side of said substrate.
 11. The chip package of claim 10 further comprising a second wirebonded wire connecting said first metal pad to said second metal pad through an opening in said substrate, and a polymer in said opening in said substrate, wherein said polymer encloses said second wirebonded wire, wherein said first semiconductor chip is over said opening in said substrate, and wherein said second metal pad is at a second side of said substrate, wherein said second side of said substrate is opposite to said first side of said substrate.
 12. The chip package of claim 10 further comprising a solder ball joined with a second side of said substrate, wherein said second side of said substrate is opposite to said first side of said substrate.
 13. The chip package of claim 10 further comprising a polymer over said first side of said substrate, wherein said polymer encloses said first wirebonded wire.
 14. The chip package of claim 10, wherein said first wirebonded wire comprises gold.
 15. A chip package comprising: a substrate; a first semiconductor chip over said substrate, wherein said first semiconductor chip has a first side facing a first side of said substrate, and wherein said first semiconductor chip comprises a first metal pad at said first side of said first semiconductor chip, wherein said first metal pad is connected to a second metal pad of said substrate; a second semiconductor chip over said first semiconductor chip, wherein said second semiconductor chip has a first side facing a second side of said first semiconductor chip, wherein said second side of said first semiconductor chip is opposite to said first side of said first semiconductor chip, and wherein said second semiconductor chip comprises a passivation layer at a second side of said second semiconductor chip, a third metal pad having a contact point at a bottom of an opening in said passivation layer, and a metal layer over said passivation layer and over said third metal pad, wherein said second side of said second semiconductor chip is opposite to said first side of said second semiconductor chip, wherein said passivation layer comprises a nitride layer having a thickness between 0.2 and 0.7 micrometers, wherein said metal layer comprises a copper layer having a thickness between 1 and 30 micrometers, wherein said metal layer is connected to said third metal pad through said opening in said passivation layer, and wherein said metal layer comprises a fourth metal pad over said passivation layer, wherein said fourth metal pad is connected to said third metal pad through said opening in said passivation layer, and wherein the position of said fourth metal pad from a top perspective view is different from that of said third metal pad, wherein said second semiconductor chip has a first edge, a second edge opposite to said first edge, and a center point between said first and second edges, wherein a horizontal distance between said fourth metal pad and said first edge is less than that between said third metal pad and said first edge, and a horizontal distance between said third metal pad and said center point is less than that between said third metal pad and said first edge; and a first wirebonded wire connecting said fourth metal pad to a fifth metal pad of said substrate across said first edge, wherein said fifth metal pad is at said first side of said substrate.
 16. The chip package of claim 15 further comprising a second wirebonded wire connecting said first metal pad to said second metal pad through an opening in said substrate, and a polymer in said opening in said substrate, wherein said polymer encloses said second wirebonded wire, wherein said first semiconductor chip is over said opening in said substrate, and wherein said second metal pad is at a second side of said substrate, wherein said second side of said substrate is opposite to said first side of said substrate.
 17. The chip package of claim 15 further comprising a solder ball joined with a second side of said substrate, wherein said second side of said substrate is opposite to said first side of said substrate.
 18. The chip package of claim 15 further comprising a polymer over said first side of said substrate, wherein said polymer encloses said first wirebonded wire.
 19. The chip package of claim 15, wherein said metal layer further comprises a nickel layer on said copper layer, wherein said nickel layer has a thickness between 1 and 10 micrometers.
 20. The chip package of claim 19, wherein said metal layer further comprises a gold layer on said nickel layer. 